Although not a fort but a Madarsa, this place is the center hub of one of the most happening places in South Delhi. A small gateway can take you back to 700 years during the reign of Alaudin Khilji who bullt a small tank here that today stands as a beautiful lake. Here is an introduction to the place in pictures because they can describe this place better than words.
Daily Passenger Travel Blog 
Yes , It is very Nice. I visited here last year